Development of cost effective methods of increasing manufacturing productivity is of prime concern in this country and others as soaring inflation and increasing foreign competition continues. One aspect of manufacturing which may be particularly sensitive to inflation and increased labor costs is assembly, which seldom occupies less than 10 percent of the labor in any industry and may require more than a third of the total work force in some instances. In an effort to reduce the number of man-hours devoted to assembly, automated devices have been developed for the assembly of mating parts or components in applications such as inserting a pin or a bolt into an orifice, shafts into bearings, bearings into bores and similar operations. More advanced automated assembly devices or robots may be programmable, and have been utilized to assemble more complicated items such as alternators for vehicle engines and similar "stack" products where all component parts can be added from a single direction.
Regardless of the sophistication of assembly machines, difficulties have been encountered in accommodating misalignment between machine or tooled parts in the assembly operation. Whether resulting from the design of the mating parts, through normal process variations or by unavoidable error, such misalignment can create wedging, jamming and damage to the parts during the assembly operation. Moreover, the mechanisms which deliver either one or both of the mating parts to a position for assembly may not provide precise registration of such parts relative to each other which could create further misalignment. Therefore, automated assembly devices must include means to correct misalignment between mating parts to avoid jamming or wedging and reduce excess insertion loading.
U.S. Pat. Nos. 4,098,001 to Watson and 4,155,169 to Drake et al are examples of prior art systems designed to accommodate misalignment between mating parts during assembly without manual manipulation and without excess insertion loading. The Watson and Drake et al patents discuss the problem of inserting a pin into a bore, and disclose systems wherein translational flexible elements and rotational flexible elements or compliances, cooperate to correct for both axial and angular misalignment between the pin and bore to permit assembly.
In the Watson system, shown in FIG. 1, the rotational flexible elements are disposed at an angle relative to the longitudinal axis of the pin to project the combined center of compliance of the system to a point along the axis of the pin remote from both the translational and rotational flexible elements. The system of Drake et al, shown in FIG. 2, includes rotational flexible elements having a center of compliance remote from the system such that the combined center of compliance of the translational and rotational flexible elements is located at or near the insertion end of the pin. Both the Watson and Drake et al systems require relatively precise positioning of the flexible elements and control of the magnitude of their compliance characteristics, particularly the rotational flexible elements, to accurately project the combined center of compliance to the desired location. Such design criteria increases the expense of the Watson and Drake et al devices, both in terms of the material and fabrication costs.
In addition, the Watson and Drake et al devices appear to be of limited use in operations involving the assembly of products having multiple parts of varying dimensions. As mentioned above, such devices project a combined center of compliance to a particular location relative to a pin or other mating part of given dimensions, to facilitate assembly. In operations where several parts of different dimensions are to be assembled, adjustment means would be needed in the Watson and Drake et al systems to assure that the center of compliance is properly located relative to each part. Such adjustment means would further add to the expense and complexity of these devices.